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車両内のLVDSデバイスの保護

Circuit Protection, Automotive

Anindita Bhattacharya

Anindita Bhattacharya

Principal Solutions Architect

米国運輸省(USDOT)と米国運輸省道路交通安全局(NHTSA)は、2018年5月1日以降、すべての自動車、SUV、トラック、バンに後方視認システムの設置を義務付ける規制を発表しました。実際に、最近までリアビューカメラは多くの車種で唯一のカメラとして使用されており、優れた安全機能だと考えられていました。現代の車両は過去数年間で大幅に進化し、死角検出、サラウンドビューモニタリング、前方および後方衝突警告、車線維持支援、自動駐車支援などの革新的な安全機能を採用しています。これらの機能はカメラとセンサーを使い、ダッシュボードのディスプレイでドライバーに車両とその周囲の状況を知らせます。現在、高級車には少なくとも6台のカメラが搭載されており、車内には、DVDプレーヤーや乗客用のテレビなどのビデオ表示システムが搭載されていることもあります。

As you can see, there is an enormous boost in the requirement for faster data and graphics communication. Low Voltage Differential Signaling (LVDS) technology is commonly used for high-speed image transmission in a vehicle (Figure 1). This blog discusses protecting the automotive LVDS nodes from electrostatic discharge (ESD) and electrical overstress (EOS) events. But first, let me briefly talk about the basics of LVDS technology.


Typical automotive LVDS connections

Figure 1. Typical automotive LVDS connections

Low Voltage Differential Signaling (LVDS)

Defined by ANSI/TIA/EIA-644 standard, LVDS is a high-speed long-distance digital interface for data communication over twisted pair cables. The LVDS architecture is shown in Figure 2. Data is transmitted between a differential transmitter and a differential receiver. A 100Ω resistor is positioned at the end of the transmission line to terminate the signal. The transmitter consists of a current source that drives a nominal 3.5mA current through the pair of cables. The LVDS transmitter, also referred to as the driver, generates the differential voltage via the termination resistor. LVDS measures the voltage difference between the inverting and noninverting signal levels on the pair of cables. This voltage difference represents a logical state.

Features of RClamp0534PWQ

Figure 2. Typical LVDS transmitter-receiver pair

Transient Protection of LVDS Devices

When designing a high-speed LVDS interface system for a severe automotive environment, it is prudent to ensure sufficient protection from EOS events. One of the primary causes of EOS is ESD. Moreover, with the shrinking size of the electronic components, it is essential to protect the members from transient threats and meet modern-day vehicles' safety and reliability requirements. ESD protection can be achieved by placing transient voltage suppressor (TVS) diodes on the LVDS differential lines to protect the interface during the fast rise time transient events. If not appropriately safeguarded, transient events can damage both the LVDS transmitter and the receiver. The data/image transmission rate of an LVDS interface is 650Mbps to 1.3Gbps. As the interface tries to transmit content while maintaining high speed, having the ESD protection device with low line-to-line capacitance is critical to ensure signal integrity.

Features of RClamp0534PWQ

Figure 3. Features of RClamp0534PWQ

Semtech's RClamp®0534PWQ is specifically designed to protect the high-speed differential lines of LVDS interfaces (Figure 3). It protects four high-speed data lines with a maximum junction capacitance of 0.18pF. It has an operating voltage of 5V and is rated for a maximum EOS Peak Pulse Current of 4A (tp=8/20µs). The typical clamping voltage at a peak current of 4A is 4.3V. RClamp0534PWQ provides transient protection as per the specification in IEC 61000-4-2 (ESD) at ±15kV (Air), ±10kV (Contact). It is also compatible with IEC 61000-4-4 (40A EFT, 5/50ns) and IEC 61000-4-5 (Lightning 4A, 8/20µs). RClamp0534PWQ is available in a 10-pin DFN package (2.5 x 1.0 x 0.55mm) with state-of-the-art side wettable flanks for automatic visual inspection (AVI) post assembly. The flow-through package design of the device simplifies the PCB layout and helps maintain signal integrity. RClamp0534PWQ can be used to protect the LVDS transmitter and receiver, as shown in Figure 4.

Protection of LVDS Tx/Rx using RClamp0534PWQ

Figure 4. Protection of LVDS Tx/Rx using RClamp0534PWQ

Semtech also offers a broad range of TVS diodes to protect automotive LVDS applications. Customers can select a TVS diode that fulfills the protection requirement of their application. Table 1 below shows the Semtech parts used for differential line protection.

Part Name VRWM Lines IEC ESD (Air/Contact) Surge (8x20µs) CL (Typ) Package
RClamp01892PWQ 1.8V 2 ±8kV (Contact) 2.5A 0.15pF DFN 1.0x0.6x0.55mm
RClamp3331PQ 3.3V 1 ±30kV/±30kV 3.5A 0.35pF DFN 1.0x0.6x0.5mm
RClamp0592PWQ 5.0V 2 ±30kV/±30kV 10A 0.55pF DFN 1.0x0.6x0.55mm
RClamp0594PWQ 5.0V 4 ±20kV/±17kV 5A 0.6pF DFN 2.5x1.0x0.55mm

 

Table 1: List of differential line protection devices from Semtech

It is common to disregard the selection of a TVS diode when redesigning an automotive system with an updated specification or speed. But with the new circuit specification or speed, the selection criteria of the TVS diode also change. Check Semtech's Automotive High Speed protection portfolio to pick the correct device for the defense of automotive high-speed data transmission in your new design. Semtech is one of the top manufacturers of TVS diodes that protects many of the world's most modern automotive electronic devices. In the severe automotive environment, careful design and proper selection of TVS diodes can't be ignored for safeguarding the communication buses and interfaces.

Please browse Semtech's Automotive Circuit Protection products to learn more about Semtech's offerings for the automotive industry.
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